Underwater turbines could turn Puget Sound’s tides into electricity

The UW recently signed an agreement with Snohomish County Public Utility District to study tidal currents in Puget Sound as a possible source of power. The Snohomish County consortium will investigate sites where turbines sitting beneath the water’s surface might use the powerful tidal currents to generate electricity.

“With renewable energy, you want to go with the source that’s most appropriate for your location on the planet,” said Phil Malte, professor of mechanical engineering and project manager. “If you’re living in Phoenix, Ariz., you want to have a strong component of solar energy in your renewable-energy mix. If you’re in the Pacific Northwest, we feel it’s appropriate to take a very hard look at tidal energy.”

The Snohomish Public Utility District holds Federal Energy Regulatory Commission study permits for locations identified as promising sites for in-stream tidal turbines. The tidal turbines look like two- or three-bladed wind turbines with a diameter of 15 feet to 60 feet. One such turbine was placed in New York City’s East River in December and five more will go down in May, according to news reports. In-stream tidal turbines sitting under the Puget Sound’s surface and rotating at very low speeds could help meet the renewable energy requirements of Initiative 937, passed by state voters in November.

The turbines would produce renewable electricity for Puget Sound communities. Funding for the study comes from the Snohomish Public Utility District and Bonneville Power Administration.

The UW’s team for this study includes faculty and graduate students from the departments of mechanical engineering, oceanography and applied mathematics. According to Malte, in the first phase of the study the team will begin to model tidal currents for the permitted sites. A third party, yet to be chosen, will measure aspects of the tidal currents relevant for producing power.

The first phase results are expected by fall of 2007 and will be followed by a second phase with more modeling and analysis of the measurements. Results will help establish whether the sites are suitable for tidal turbines and how much power such systems could generate. The study will look at environmental and economic impacts, Malte said.

It’s too early to say how much total energy the tidal turbines might produce, Malte said. Related research will calculate how much energy an estuary like Puget Sound could produce before turbines would begin to lower the height of the tides in Puget Sound or reduce the volume of water that Puget Sound exchanges with the ocean. The mechanical engineering’s program on renewable tidal energy receives ongoing support from the Electric Power Research Institute.